ML17219A332

Forwards Response to 861125 Request for Addl Info Re Reanalysis of Reactor Coolant Pump Seized Rotor & Loss of Nonemergency Ac Power.Seized Rotor Causes Asymmetric Primary Flow Through Steam Generators

ML17219A332
Person / Time
Site:	Saint Lucie
Issue date:	01/29/1987
From:	Woody C FLORIDA POWER & LIGHT CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
L-87-31, NUDOCS 8702050441
Download: ML17219A332 (21)

Text

.ACCESSION NBR FAC IL: 50-335 AUTH. NAI'lE WOODY> C. O.

REC IP. NAI'1E REGULATORY

-QRNATION DISTRIBUTION BY1'i (RIDS) 8702050441 DQC. DATE: 87/01/29 NOTARIZED-NO St.

Lucie Plant>

Unit 1> Florida Power 8c Light Co.

AUTHOR AFFILIATIQN Fl ov ida Powev Zc Lig ht Co.

RECIPIENT AFFILIATION Document Contv ol Branch (Document.Control Desk )

DOCKET 0 05000335

SUBJECT:

Fovwav'ds response to 861125 request fov'ddi info re v'eanalgsis of v eactov coolant pump seized rotov 5 loss of nonemergencg ac powev. Seized rotor causes asgmmetri c primav g flow thv ough steam genev'ators.

DISTRIBUTION CODE:

A001D COPIES RECEIVED: LTR ENCL SIZE:

TITLE:

QR Submittal:

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FLORIDAPOWER & LIGHTCOMPANY JANUARY 89 1987 L-87-3 I U. S. Nuclear Regulatory Commission Document Control Desk Washington, D. C. 20555 Gent lemen:

Re:

St. Lucie Unit I Docket No. 50-335 Reanalysis of RCP Seized Rotor and Loss of All Non-Emer enc AC Power By letter dated November 25, l986 (E. G. Tourigny to C. O. Woody), the NRC staff forwarded to Florida Power & Light Company (FPL) a request for additional information (RAI) regarding a reanalysis of reactor coolant pump (RCP) seized rotor and loss of'all non-emergency AC power (SR/LOOP).

These questions resulted from the staff's review of FPL letters L-82-38I, dated August 3l, l982 and L-84-246, dated September I I, l984 pertaining to the St. Lucie Unit I stretch power authorization.

Attached are FPL's responses to the staff's November 26, I 986 RAI.

The due date for FPL's response was extended to January 3l, l987 by FPL letter L-86-'5I8; dated December 22, l 986 as agreed to by the NRC staff.

s Please contact us if you have any questions about this submittal.

Very truly yours, C. O. Woo Group V'esident Nuclear nergy COW/EJW/gp Attachrnent cc:

Dr. J. Nelson Grace, Region II, USNRC Harold F. Reis, Esquire

, 870205044 k '701'29

. PDR 'DOCK '05000335 I

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ATTACHMENT Responses to NRC Questions Regarding RCP Seized Rotor and Loss of AllNon-Emergency AC Power EJW3/0 I5/2

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Question:

The Staff finds that the response to question 3c of Reference I is unclear.

With regard to the analyses of the reactor coolant pump (RCP) seized rotor event and the loss of all non-emergency AC power event, the following statement is made:

"As a result, both steam generators depressurize virtually at the same rate, showing no apparent asymmetry.

However, since the affected steam generator discharges more steam through the stuck open ADV than the unaffected steam generator due to its proximity to that valve, its level reaches the AFW actuation setpoint; initiating the delivery of the AFW following a 2 minute time delay."

These two sentences appear to the Staff to be contradictory.

If both steam generators depressurize at virtually the same

rate, how could more steam be discharged from one than the other?

Wouldn't the wafer level in the two steam generators have to be the same?

This apparent discrepancy should be explained.

Specifically, time dependent plots of the various important parameters, e.g.,

steam generator pressure and level, main and auxiliary feedwater flow, and steam flow should be provided to support the response.

Response

Figures I through 5, respectively, are plots of steam flow, main feedwater flow, auxiliary feedwater flow, steam generator

pressure, and steam generator liquid water mass for the RCP seized rotor with a stuck open ADV and loss of AC event.

Figures 6 through IO are plots of these same parameters for the loss of all non-emergency AC power with a stuck open ADV event.

During the first 30 minutes of both of these transients, the pressures in the steam generators remain above the Main Steam Isolation Signal (MSIS) setpoint (578 psia).

As such, the affected and unaffected steam generators "communicate" via the main steam line header that is common to them.

Therefore, the two steam generators depressurize at virtually the same rate, showing no apparent asymmetry.

The steam generator presssure response is shown in Figures 4 and 9 for the RCP seized rotor and the loss of all non-emergency AC power events, respectively.

The asymmetry in steam generator liquid water mass (shown in Figures 5 and IO) is due to asymmetric steam generator steam flow (shown in Figures I and 6). This is a result of the pressure drop between the affected steam generator and the stuck open ADV being less than the pressure drop between the unaffected steam generator and the stuck open ADV. The heat transfer in the steam generators and the primary flow through the steam generators (the primary side being in natural circulation) will support the asymmetric behavior of the steam flow and level response in the steam generators.

However, because of the main steam line header link, the steam generator s secondary sides are maintained at virtually the same pressure and temperature (the steam generator secondary is saturated).

The seized rotor additionally causes asymmetric primary flow through the steam generators, which results in increased asymmetry in steam generator heat transfer and hence increased asymmetry in steam flow for the RCP seized rotor event.

ln conclusion, since the main steam line header links the steam generators, nearly symmetric steam generator pressures are calculated.

However, because of the asymmetry in steam generator heat transfer and steam flow, there is asymmetry in the steam generator water mass.

This results in the affected steam generator reaching the AuxiliaryFeedwater (AFW) actuation setpoint sooner.

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Question:

Reference 2 approved an AFW delivery time delay of greater than 2 minutes.

Please address the different assumptions on feedwater delivery time and describe how the Reference 2 assumption affects the conclusions in the analyses associated with the RCP seized rotor and the loss of all non-emergency AC power events.

Response

An increase in the auxiliary feedwater actuation time delay would not significantly impact the RCP seized rotor or the loss of all non-emergency AC power events.

For these events, the peak primary and secondary pressures occur long before auxiliary feedwater flow begins.

As described below, an increase in the auxiliary feedwater actuation time delay would not significantly impact the total amount of steam released or the calculated offsite dose.

As shown in Figures 3 and 5 for the seized rotor event, and Figures 8 and IO for the loss of AC event, auxiliary feedwater flow is initiated when the steam generator level falls below the auxiliary feedwater actuation signal (AFAS) setpoint and the flow is turned off when the steam generator water level rises above the level that causes auxiliary feedwater cutoff.

Prior to AFW actuation, steam flows from both the steam generators are stable (see Figures I

and 6).

For the loss of all non-emergency AC power event, initiation of auxiliary feedwater does not significantly affect the steam flow. As

such, an increase in the auxiliary feedwater actuation time delay would not significantly affect the total steam release and offsite dose.

For the RCP seized rotor event the steam flow from the affected steam generator (which receives auxiliary feedwater) decreases slightly following AFW actuation.

Meanwhile, the steam flow from the unaffected generator (which does not receive auxiliary feedwater during the first 30 minutes) increases an amount that roughly offsets the decrease in steam flow from the affected steam generator.

An increase in the auxiliary feedwater actuation time delay would merely cause the contribution of each steam generator's steam flow to the total steam flow to change slightly, with no significant effect on the total steam release and offsite dose.

In conclusion, the total reported doses for these events would remain only a small fraction of the IO CFR l00 limits.

References (I)

NRC letter to C.

O.

Woody (FPL), "Reanalysis of RCP Seized Rotor and Loss of All Non-Emergency AC Power",

November 25, I 986.

(2)

NRC letter from D. E. Sells to C. O. Woody (FPL),

January l5, I986.

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FIGURE 1 ST. LUCIE UNIT 1 SEIZED RCP ROTOR W/LOACAND STUCK OPEN ADV 1600 1200 u

m 800 0I-Rm400 (gZ; UNAFFECTED SG 0

-400 AFFECTED SG 0

200 400 600 800 1000 TIME, SECONDS 1200 1400 1600 1800

FIGURE 2 ST. LUCIE UNIT 1 SEIZED RCP ROTOR W/LOACAND STUCK OPEN ADV 2000 1600 0

1200 I-0 800 z

AFFECTED UNAFFECTED 400 0

200 400 600 800 1000 1200 1400

'1600 1800 TIME, SECONDS

FIGURE 3 ST. LUCIE UNIT 1 SEIZED RCP ROTOR W/LOACAND STUCK OPEN ADV 2000 Pu 1600 0

1200 I-D 800 XD.

400 e

AFFECTED SG 00 200 400 600 800 1000 1200

1400, 1600 1800 TIME, SECONDS

1200 UNAFFECTED SG FIGURE 4 ST. LUCIE UNIT 1 SEIZED RCP ROTOR W/LOACAND STUCK OPEN ADV 1000 AFFECTED SG 800 CO K

D ca 600 C9 400 200 0 0 200 400 600 800 1000 1200 1400 1600 1800 TIME, SECONDS

200,000 FIGURE 5 ST. LUCIE UNIT 1 SEIZED RCP ROTOR W/LOACAND STUCK OPEN ADV cQ 180,000 Z

K 160,000 Q

Da O

140,000 I-C9 cZ 120,000 UNAFFECTED SG AFFECTED SG 100,000 AFAS GENERATED 0

800 1000 1400 1800 TIME, SECONDS

FIGURE 6 ST. LUCIE UNIT 1 LOSS OF AC W/STUCK OPEN ADV 1600 u

g 1200 0

1000 4

0 400 C9 I-0 AFFECTED SG UNAFFECTED SG

-400 0

200 400 600 800 1000 1200 1400 1600 1800 TIME, SECONDS

2000 FIGURE 7 ST. LUCIE UNIT 1 LOSS OF AC W/STUCK OPEN ADV 1600 u

1200 0

K, 800 z

AFFECTED SG UNAFFECTED SG 400 0

200 400 600 800 1000 1200 1400 1600 1800 TIME, SECONDS

2000 FIGURE 8 ST. LUCIE UNIT 1 LOSS OF AC W/STUCK OPEN ADV o

1600 Z

0 1200 I-O 800 XD 400 AFFECTED SG UNAFFECTED SG 0

200 400 600 800 1000 1200 1400

'I600 1800 TIME, SECONDS

1200 FIGURE 9 ST. LUCIE UNIT 1 LOSS OF AC W/STUCK OPEN ADV AFFECTED SG 1000 800 KD 600 I-K Q

400 UNAFFECTED SG 200 0

200 400 600 800 1000 TIME, SECONDS 1200 1400 1600 1800

200,000 FIGURE 10 ST. LUCIE UNIT 1 LOSS OF AC W/STUCK OPEN ADV 180,000 160,000 UNAFFECTED SG 140,000 AFFECTED SG AFAS GENERATED 120,000 AFAS GENERATED 100,000 0

200 400 600 800 1000 TIME, SECONDS

'1200 1400 1600 1800